The present invention generally relates to an apparatus and a method for aligning a loadport on a process machine and more particularly, relates to an apparatus for aligning a loadport on a process machine which consists of a base plate and an alignment block with an aperture therethrough for passage of an alignment laser beam and a method for using the apparatus.
In the fabrication of a product, the product is usually processed at many work stations or processing machines. The transporting or conveying of partially finished products, or work-in-process (WIP) parts, is an important aspect in the total manufacturing process. The conveying of semiconductor wafers is especially important in the manufacturing of integrated circuit chips due to the delicate nature of the chips. Furthermore, in fabricating an IC product, a multiplicity of fabrication steps, i.e., as many as several hundred, is usually required to complete the fabrication process. A semiconductor wafer or IC chips must be transported between various process stations in order to perform various fabrication processes.
For instance, to complete the fabrication of an IC chip, various steps of deposition, cleaning, implantation, etching and passivation must be carried out before the chip can be packaged for shipment. Each of these fabrication steps must be performed in a different process machine, i.e. a chemical vapor deposition chamber, an ion implantation chamber, an etcher, etc. A partially processed semiconductor wafer must be conveyed between various work stations many times before the fabrication process is completed. The safe conveying and accurate tracking of such semiconductor wafers or work-in-process parts in a semiconductor fabrication facility is therefore an important aspect of the total fabrication process.
Conventionally, partially finished semiconductor wafers or WIP parts are conveyed in a fabrication plant by automatically guided vehicles or overhead transport vehicles that travel on predetermined routes or tracks. For the conveying of semiconductor wafers, the wafers are normally loaded into cassettes pods, such as SMIF (standard machine interface) or FOUP (front opening unified pod), and then picked up and placed in the automatic conveying vehicles. For identifying and locating the various semiconductor wafers or WIP parts being transported, the cassettes or pods are normally labeled with a tag positioned on the side of the cassette or pod. The tags can be read automatically by a tag reader that is mounted on the guard rail of the conveying vehicle.
In an automatic material handling system (AMHS), stockers are used in conjunction with automatically guided or overhead transport vehicles, either on the ground or suspended on tracks, for the storing and transporting of semiconductor wafers in SMIF pods or in wafer cassettes. For instance, three possible configurations for utilizing a stocker may be provided. In the first case, a stocker is utilized for storing WIP wafers in SMIF pods and transporting them first to tool A, then to tool B, and finally to tool C for three separate processing steps to be conducted on the wafers. After the processing in tool C is completed, the SMIF pod is returned to the stocker for possible conveying to another stocker. The configuration in the first case is theoretically workable but hardly ever possible in a fabrication environment since the tools or processing equipment cannot always be arranged nearby to accommodate the processing of wafers in the stocker.
In the second case, a stocker and a plurality of buffer stations A, B and C are used to accommodate different processes to be conducted in tool A, tool B and tool C. A SMIF pod may be first delivered to buffer station A from the stocker and waits there for processing in tool A. Buffer stations B and C are similarly utilized in connection with tools B and C. The buffer stations A, B and C therefore become holding stations for conducting processes on the wafers. This configuration provides a workable solution to the fabrication process, however, requires excessive floor space because of the additional buffer stations required. The configuration is therefore not feasible for use in a semiconductor fabrication facility.
In the third case, a stocker is provided for controlling the storage and conveying of WIP wafers to tools A, B and C. After a SMIF pod is delivered to one of the three tools, the SMIF pod is always returned to the stocker before it is sent to the next processing tool. This is a viable process since only one stocker is required for handling three different processing tools, and in that no buffer station is needed. This configuration illustrates that the frequency of use of the stocker is extremely high since the stocker itself is used as a buffer station for all three tools. The accessing of the stocker is therefore more frequent than that required in the previous two configurations.
FIG. 1 illustrates a schematic of a typical automatic material handling system 20 that utilizes a central corridor 22, a plurality of bays 24 and a multiplicity of process machines 26. A multiplicity of stockers 30 are utilized for providing input/output to bay 24, or to processing machines 26 located on the bay 24. The central corridor 22 designed for bay lay-out is frequently used in an efficient automatic material handling system to perform lot transportation between bays. In this configuration, the stockers 30 of the automatic material handling system become the pathway for both input and output of the bay. Unfortunately, the stocker 30 frequently becomes a bottleneck for internal transportation. It has been observed that a major cause for the stockers 30 to be the bottleneck is the input/output ports of the stockers.
In modern semiconductor fabrication facilities, especially for the 200 mm or 300 mm FAB plants, automatic guided vehicles (AGV) and overhead hoist transport (OHT) are extensively used to automate the wafer transport process as much as possible. The AGV and OHT utilize the input/output ports of a stocker to load or unload wafer lots, i.e. normally stored in POUFs. FIG. 2 is a perspective view of an overhead hoist transport system 32 consisting of two vehicles 34,36 that travel on a track 38. An input port 40 and an output port 42 are provided on the stocker 30. As shown in FIG. 2, the overhead transport vehicle 36 stops at a position for unloading a FOUP 44 into the input port 40. The second overhead transport vehicle 34 waits on track 38 for input from stocker 30 until the first overhead transport vehicle 36 moves out of the way.
Similarly, the OHT system is used to deliver a cassette pod such as a FOUP to a process machine. This is shown in FIG. 3. A cassette pod 10 of the FOUP type is positioned on a loadport 12 of a process machine 14. The loadport 12 is frequently equipped with a plurality of locating pins 16 for the proper positioning of the cassette pod 10. A detailed perspective view of the FOUP 10 is shown in FIG. 4. The FOUP 10 is constructed by a body portion 18 and a cover portion 28. The body portion 18 is provided with a cavity 46 equipped with a multiplicity of partitions 48 for the positioning of 25 wafers of the 300 mm size. The body portion 18 is further provided with sloped handles 50 on both sides of the body for ease of transporting. On top of the body portion 18, is provided with a plate member 52 for gripping by a transport arm (not shown) of the OHT system (not shown).
When an OHT system is utilized to transport a cassette pod to a process machine, problems arise when the loadport of the process machine is not in alignment with the OHT system. Mis-positioned cassette pods on a loadport not only affects the operation of loading/unloading from the pod, but also in severe instances may cause the cassette pod to tip over and cause breakage of the wafers. Conventionally, a laser surveying instrument is used to align the cassette pod, i.e. or the loadport of the process machine, to an OHT system. While the laser equipment may be properly used in a pilot plant setup, it cannot be practically used in a fabrication facility for several reasons. First, the laser equipment is costly and difficult to operate. Secondly, the laser emission is harmful to human eyes and thus when used, disturbs other operators that are working in the same intra-bay. In a production facility, there are frequently 20 or 30 process machines lined up in an intra-bay area. It is therefore difficult or impossible to use laser for aligning one machine, while not disturbing the operations of the other machines.
In a new fabrication facility for 300 mm wafers, the OHT system is the most popularly used cassette transport system. It is therefore very important to be able to align all the cassette pods or the loadports of the process machine in a straight line in the same OHT intra-bay to assure the integrity of the fabrication process. To ensure minimum disturbance to the fabrication process, s the laser alignment equipment cannot be used in a fabrication facility for the alignment of a single process machine.
When installing a process machine, the center of the loadport of the machine must be aligned not only with an overhead hoist transport system, but also with the other loadports on the neighboring process machines in order to assure the accurate delivery of a cassette pod to the loadport. Conventionally, the loadport center is aligned manually by making mechanical measurements and by subsequent manual calibration. The manual alignment process is tedious, time consuming and inaccurate.
It is therefore an object of the present invention to provide an apparatus for aligning a loadport on a process machine that does not have the drawbacks or shortcomings of the conventional apparatus.
It is another object of the present invention to provide an apparatus for aligning a loadport on a process machine that is a simple mechanical device.
It is a further object of the present invention to provide an apparatus for aligning a loadport on a process machine that utilizes an alignment block provided with an aperture extending longitudinally through the block.
It is still another object of the present invention to provide an apparatus for aligning a loadport on a process machine that utilizes an alignment block with an aperture therethrough and an optical source.
It is yet another object of the present invention to provide an apparatus for aligning a loadport on a process machine which includes an alignment block with an aperture therethrough, a light source and an optical detector.
It is still another further object of the present invention to provide a method for aligning a loadport on a process machine that can be carried out by projecting a light beam through a small aperture in an alignment block mounted on the loadport.
In accordance with the present invention, an apparatus and a method for aligning a loadport on a process machine are provided.
In a preferred embodiment, an apparatus for aligning a loadport on a process machine can be provided which includes a base plate that has a planar top and bottom surface parallel to each other, the base plate has at least two vertical through holes adapted for mating to at least two locating pins on a top surface of the process machine; an alignment block which has a planar bottom surface that intimately mates the top planar surface of the base plate, the alignment block has an aperture extending longitudinally therethrough parallel with the bottom surface of the alignment block, the aperture has an entrance end, an exit end and an inside diameter not larger than 5 mm; a light source positioned juxtaposed to the entrance end of the aperture; and an optical detector situated to the exit end of the aperture for detecting any light transmitted through the aperture.
In the apparatus for aligning a loadport on a process machine, the aperture may be formed in a T-shape extending longitudinally and transversely through the alignment block with an image splitter mounted at an intersection of the T. The image splitter may be a mirror, while the alignment block may be integrally formed with the base plate. The base plate and the alignment block may be fabricated of a rigid material, or may be fabricated of a rigid plastic or aluminum. The light source may be a laser source, or a laser source that operates in a pulse mode. The alignment block may have a length not more than 150 mm, while the aperture in the alignment block may have a diameter not larger than 3 mm.
The present invention is further directed to a method for aligning a loadport on a process machine which can be carried out by the operating steps of: providing a base plate that has a planar top and bottom surface parallel to each other; mounting the base plate to a process machine by engaging at least two vertical through holes to at least two locating pins on a top surface of the process machine; providing an alignment block which has an aperture extending longitudinally therethrough parallel with a bottom surface of the alignment block, the aperture having an entrance end, an exit end and an inside diameter not larger than 5 mm; mounting the alignment block on the base plate by engaging a planar bottom surface of the block intimately to the top planar surface of the base plate; projecting a light beam into the entrance end of the aperture; and detecting any light transmitted through the aperture at the exit end of the aperture.
The method for aligning a loadport on a process machine may further include the step of forming the aperture in a T-shape extending longitudinally and transversely through the alignment block with an image splitter mounted at an intersection of the T. The method may further include the step of providing the image splitter in a mirror, or the step of forming the alignment block integrally with the base plate, or the step of fabricating the base plate and the alignment block in a rigid material, such as plastic or aluminum. The method may further include the step of providing the light source in a laser source form or as a laser source that operates in a pulse mode. The method may further include the step of forming the alignment block to a length not more than 150 mm, or the step of forming the aperture in the alignment block to a diameter not larger than 3 mm.